1. Field of the Invention
The present invention relates to a method of and an apparatus for shaping a fibrous elastic body which is, for example, used for a seat back pad, a seat cushion pad, or a pad, etc., of a seat for an automobile.
2. Description of the Related Art
Molded polyurethane foam is in popular use, for example, as a material for a seat back pad, a seat cushion pad, etc., of a seat for an automobile. However, in recent years, a fibrous elastic body, due to its excellent recyclability, has attracted more attention than shaped polyurethane foam which is inferior in terms of recyclability. Such a fibrous elastic body is shaped by a laminate shaping technique or a blow shaping technique which will be described below.
First, the laminate shaping technique will be described. Before describing the technique, a technique for shaping a matted fiber material which is used for the laminate shaping technique will be described with reference to the explanatory diagrams in FIG. 15(a) through FIG. 15(e). In FIG. 15(a), a matrix fiber which is made of a polyester fiber and a binder fiber which is made of a polyester fiber which has a lower melting point than that of the matrix fiber are prepared. Next, in FIG. 15(b), the matrix fiber and the binder fiber are cotton-blended. Next, in FIG. 15(c), the cotton-blended fibers are fibrillated (or opened), thereby obtaining a fibrillated fiber material 100. Then, in FIG. 15(d), the fibrillated fiber material 100 is matted, thereby obtaining a matted fiber material 101 which has a certain thickness with a certain density. Next, in FIG. 15(e), the matted fiber material 101 is cut into a predetermined shape, whereby a cut fiber material (or "a fibrous mat material") 102 is obtained. On average, a number of cut-out pieces for a seat back pad is 6 to 8.
Now, a shaping die which is used for laminate type shaping will be described with reference to FIG. 14(a) through FIG. 14(d) which shows the shaping process. A shaping die 130 includes a bottom die 131 and a top die 135 which are approximately box-like in shape. In FIG. 14(a), the top die 135 is omitted. The bottom die 131 and the top die 135 have shaping surfaces 131a and 135a, respectively, which define a predetermined shape, i.e., a cavity of a seat back pad when the shaping die is closed. The respective shaping surfaces 131a and 135a of the bottom die 131 and the top die 135 are formed by a highly breathable punching metal which includes a number of holes. The shaping surface 131a of the bottom die 131 forms a front surface portion of the seat back pad. The shaping surface 135a of the top die 135 forms a back surface portion of the seat back pad. An air supply slot 133 is formed at the bottom surface of the bottom die 131. On the other hand, an exhaust slot 136 is formed at the top surface of the top die 135.
To shape a seat back pad using the shaping die 130 described above by the laminate-type method, in FIG. 14(a), the fibrous mat material 102 described earlier is disposed as a laminate, within the shaping surface 131a of the bottom die 131 which is opened. Next, in FIG. 14(b), the top die 135 is closed over the bottom die 131 to thereby clamp the fibrous mat material 102. In this condition, heated air is force-fed inside the bottom die 131 through the air supply slot 133 of the bottom die 131. After being blown through the fibrous mat material 102, the heated air is discharged outside through the top die 135 at the exhaust slot 136. Heating with the heated air melts the binder fiber which is contained in the fibrous mat material 102, whereby the matrix fiber is shaped into the shape of a seat back pad. Following this, in FIG. 14(c), instead of the heated air, cool air is blown through the fibrous mat material 102 to thereby cool the fibrous mat material 102. This solidifies the melted binder fiber. Next, in FIG. 14(d), the shaping die is opened and the content is removed from the shaping die, whereby a seat back pad 110 is obtained.
Now, the blow shaping technique will be described with reference to the explanatory diagram in FIG. 16. A shaping die 140 which is used in this type of shaping is almost the same as the shaping die which is used in the laminate shaping technique described above, and therefore, identical reference symbols will be assigned to identical or corresponding portions. A redundant description will be omitted, and different portions will be described. The bottom die 131 and the top die 135, as they are opened, are enclosed by a restriction box 141 which is formed by a punching metal. The bottom die 131 includes a material blowing slot 132 which leads to an inner space which is created between the bottom die 131 and the top die 135 as they are opened. Unlike the laminate-type method, the blow-type method uses the fibrillated fiber material 100 which is obtained during the course of shaping of the fibrous mat material 102 (See FIG. 15(c)), instead of using the fibrous mat material 102.
To shape a seat back pad using the shaping die 140 as described above by the blow-type method, in FIG. 16, the inner space between the bottom die 131 and the top die 135 is filled with the fibrillated fiber material 100 by means of air feeding under a pressure feed force, that is, air blown, through the material blowing slot 132 of the bottom die 131. Following this, the fibrillated fiber material 100 is clamped, with the top die 135 fit with the bottom die 131. Next, through steps which are similar to the shaping process of the laminate-type method (See FIG. 14(b) through FIG. 14(d)), the seat back pad 110 is obtained.
The laminate shaping technique described above, requiring to set the fibrous mat material 102 inside the shaping die 130 depending on necessity, ensures an advantage that it is possible to shape a material which has a complex shape including a vertical wall portion, a pocketform portion, etc., without creating any significant defective shape due to density shortage or filling shortage. Another advantage is that it is possible to set a non-woven fabric, a pendant wire and the like, which are to be attached to the back surface of the seat cushion pad 110, in the shaping die 130 together with the fibrous mat material 102 and to simultaneously shape them.
However, in the laminate shaping technique, in order to suppress a density change at a joint portion where the fibrous mat material 102 is disposed overlapping, about 6 to 8 cut-out pieces are necessary as described earlier. Hence, it is necessary to cut the matted fiber material 101 and consequently form about 6 to 8 pieces of the fibrous mat material 102, and set the cut fibrous mat materials 102 one after another to the bottom die 131. This creates a problem where productivity is very bad.
Meanwhile, according to the blow shaping technique, since it is not necessary to cut the matted fiber material 101 and set the fibrous mat materials 102 to the bottom die 131, which is required in the laminate shaping technique, the problem of bad productivity is solved. In addition, since the blow shaping technique rarely creates a defective shape due to density shortage and filling shortage if an article to be shaped has a simple shape such as a cubic shape and a rectangular shape, the blow shaping technique is appropriate. However, when an article to be shaped has a complex shape which includes a vertical wall portion, a pocketform portion, etc., the blow shaping technique creates defective shape problem due to density shortage or filling shortage, as will be described in detail below.
Density shortage will be described with reference to the explanatory diagrams in FIG. 17(a) and FIG. 17(b). In FIG. 17(a), a fiber density of the fibrillated fiber material which is filled by blowing into the inner space which is created between the bottom die 131 and the top die 135 as they are opened is approximately constant.
At this stage, it is assumed that a thickness B1 of a general portion of the seat back pad is 3, a thickness A1 of vertical wall portions on the left-hand and the right-hand sides (i.e., portions which include a side support portion and an edge portion of the seat back pad) is 5, and fiber densities of the respective portions are both 1. Assuming that a clamping volume C at clamping of the fiber material with shaping die closed is 2, the thickness A of the vertical wall portions is:
A=(A1-C)/A1=3/5 PA1 B=(B1-C)/B1=1/3
The fiber density accordingly changes to 5/3. Meanwhile, the thickness B of the general portion is:
The fiber density accordingly changes to 3. Therefore, the fiber density D1 of the vertical wall portions is as low as 5/9 of the fiber density D2 of the general portion, thereby creating a defective shape due to density shortage. Because of this, with the blow shaping technique, it is difficult to increase the rigidity of the side support portion which demands a higher rigidity, due to a necessity related to side supportability or the like, than in the case of the general portion.
Next, filling shortage is described with reference to the explanatory diagrams in FIGS. 18(a), 18(b) and 18(c). Among the diagrams, FIG. 18(a) is a cross sectional view showing a condition in which the fibrillated fiber material 100 is filled in the shaping die 140, FIG. 18(b) is a cross sectional view showing a condition of the shaping die 140 of FIG. 18(a) as it is closed, and FIG. 18(c) is a cross sectional view showing another example of the shaping die 140. As in the case of the shaping die 140 as that shown in FIG. 18(b) which includes an under portion 134 where the bottom die 131 is in an undercut state with respect to a parting line PL, as shown in FIG. 18(a), since the fibrillated fiber material 100 to be filled in by blowing does not easily reach the under portion 134 of the bottom die 131, filling shortage of the fiber material 100 results. It then follows that even when the die is closed and the fibrillated fiber material 100 is clamped, as shown in FIG. 18(b), it is not possible to avoid a decrease in the density in the under portion 134 of the bottom die 131, which in turn creates a defective shape. Meanwhile, when the parting line PL is set at a position which corresponds to an outer most position of the seat back pad and the under portion 134 is accordingly excluded as shown in FIG. 18(c), a trace of the parting line PL easily appears in a design surface of the seat back pad product. This creates a necessity to post-process the trace, which is an increase in cost and not desirable.
Another example of filling shortage will be described with reference to the explanatory diagrams in FIGS. 19(a) and 19(b). Among the diagrams, FIG. 19(a) is a cross sectional view showing a condition in which the fiber material 100 is filled in the shaping die 140, while FIG. 19(b) is a cross sectional view showing a condition of the shaping die 140 of FIG. 19(a) as it is closed. In FIG. 19(a), when the top shape 135 includes a recess portion 137 which corresponds to a pocketform back lining top portion (or "a pocketform portion") which is formed above the seat back pad, the fibrillated fiber material 100 which is filled in by blowing through the material blowing slot 132 of the bottom die 131 does not easily enter the recess portion 137, which in turn results in filling shortage of the fiber material 100. Therefore, it is not possible to avoid a decrease in the density within the recess portion 137 even though the die is closed and the fibrillated fiber material 100 is clamped, thereby creating a defective shape.